1. Field of the Invention
The present invention generally relates to vide encoders for encoding video data in real time, and particularly relates to a vide encoder provided with the function to extract an image from the video data.
2. Description of the Related Art
In recording equipment such as hard-disk recorders or the like, an analog input NTSC video signal is MPEG-encoded, and the encoded video data is recorded on a hard disk or the like.
To be specific, an analog input NTSC video signal is converted into the ITU-R656 format by use of an NTSC decoder, and the converted video data is supplied to an MPEG2 encoder. The supplied video data is written to a frame memory externally attached to the MPEG2 encoder via a frame synchronizer provided in the MPEG2 encoder. The frame memory has a plurality of banks (e.g., three banks). A bank to which data is written is successively specified, and the bank having the oldest data stored therein is overwritten by use of new data.
Analog input audio signals are converted into the I2S format by use of an audio ADC (analog-to-digital converter), and the converted audio data is supplied to the MPEG2 encoder.
Among the frame data written to the plurality of banks of the frame memory, the frame data of the oldest bank is read from the frame memory by the MPEG2 encoder. The read frame data is transferred via the frame synchronizer provided in the MPEG2 encoder to an MPEG2 video encode unit for encoding into the MPEG2 video MP@ML format. Further, the audio data is encoded into data in the MPEG1 audio-layer-2 format. The system multiplexer provided in the MPEG2 encoder multiplexes the video stream and audio stream obtained in this manner into the MPEG2-PS format for output as a multiplexed stream to an exterior of the MPEG2 encoder via the 8-bit dedicated port.
The stream output from the MPEG2 encoder is recorded on the hard disk via an IDE-I/F.
In such a manner as described above, vide contents such as television programs, movies, and the like are stored in the hard disk as separate files. Recording equipment such as hard-disk recorders or the like may sometimes use small-sized thumbnail images for the purpose of managing these files. When a list of files corresponding to respective video contents are to be presented to the user, for example, thumbnail images corresponding to the files may be displayed, thereby allowing the user to identify the contents of the files easily.
Thumbnail images are generated by obtaining 360-×-240 pixels, for example, by subsampling image data of 720-×-480 pixels, which correspond to the valid image area of the ITU-R656-format video data. The microcomputer embedded in a hard-disk recorder or the like generates such thumbnail images for the purpose of managing file information, and stores these thumbnail images in memory such as a RAM.
In order to generate a thumbnail image, there is a need to extract one image from the video data output from the NTSC decoder, for example, for transfer to the microcomputer. In such a case, a dedicated circuit needs to be provided to extract an image from the video data output from the NTSC decoder, which leads to a cost increase with respect to the system.
It is also conceivable to use the MPEG2 encoder to extract an image from the frame memory. This requires a dedicated function to be newly implemented. When three banks are provided in the frame memory, there is a need to read an image from one of the banks for use in creating a thumbnail image separately from the encoding process while this ongoing encoding process keeps writing and reading data to/from the three banks. One frame of the NTSC video data is 33 ms, so that the bank from which data is read for creation of a thumbnail image will be overwritten unless the data is read within the 66-ms period during which writing is performed with respect to the two other banks. This makes it necessary to give high priority to the process of reading an image for creation of a thumbnail, which ends up necessitating special control procedures, and affects the ongoing encoding operation.
Accordingly, there is a need for an MPEG encoder that can extract image data from video data for transfer to a microcomputer without affecting the encoding operation.